Effective personal adaptation and social life depend on our ability to discern our own actions and thoughts from those of others. This is not always a simple discrimination, and it is fortunate that our own actions and thoughts are usually marked with a unique feeling, an experience of conscious will. This feeling separates our actions and thoughts from those that seem to have been done or thought by others or caused by events in the world. This research tests a theory of apparent mental causation, which suggests that this experience of conscious will arises when we infer that our thoughts have caused our actions. According to this theory, we are likely to experience conscious will for what we do when we have thoughts that are consistent with what we do, when these thoughts occur just before what we do, and when other potential causes of what we do are not obvious to us. These principles of consistency, priority, and exclusivity suggest why and when people might experience conscious will erroneously--feeling that they controlled an action, for example, when they did not, or feeling that they did not perform an action when in fact they did. Seventeen studies examine conditions that create these illusions by testing the role of these principles in the experience of conscious will. They focus on this experience in everyday actions, as well as in laboratory settings that allow the precise determination of the influence of the principles. Some of the studies test the principles in the case of the vicarious experience of will for the actions of others, and others examine how these principles can yield an understanding of unwilled actions. A final set of studies explores the relationship between processes of action production and processes underlying the experience of will. One such study investigates a clinical application of the theory by assessing how patients with obsessive-compulsive disorder can be influenced to understand their own mental control processes, and so to reduce the intrusive thoughts and unwilled actions that are symptoms of this disorder.